Most automobiles manufactured and sold today are factory equipped with various types of audio sound systems. For example, it is common to have an AM/FM radio factory installed as standard equipment. Optional components may include a cassette player, a compact disc player, a television, a television/video cassette player combination, and digital video disc player/viewer. An essential component to these various systems are speakers.
Upon completion of the installation of the entire audio or audio/visual system, some form of an audio test is conducted to verify that the speakers are connected properly. Test conditions are limited and historically were limited to turning on the radio and listening to each speaker.
Later techniques coupled vehicle alignment with audio testing in order to better utilize plant floor space and reduce test variances. Reduction in manual testing was important to reduce costs. Additionally, testing in a noisy manufacturing environment was difficult.
One method, described in U.S. Pat. No. 5,361,305, is applicable to an audio system which is coupled to a vehicle data bus. The data bus is accessible for coupling to an external controller. The test system is fully automatic and uses the vehicle data bus commands to control the audio system and monitor its response to radio frequency test signals in the presence of high ambient noise. The test checks all speakers and associated harness for proper connection and function. The computer exercises audio control functions and monitors test results through a controlled radiation pattern modulated by an encoded test signal, which is used to provide an RF test signal in close proximity to the vehicle antenna base.
The test sequence includes exercising AM and FM Seek functions to find the generated RF signals, thereby ensuring the integrity of the cabling and antenna connections. Additionally, Fade and Balance settings are tested to select and positively identify each speaker individually, for example by zone, such as left front, left rear, right front and right rear. Additional speakers of significantly different frequency ranges can also be tested one at a time to verify proper connection within a zone. A sine wave or warble tone is output by the speakers which is then received by a microphone placed in the vehicle. The tone received by the microphone is processed by a digital signal processor, and a single decibel level is calculated independent of the number of speakers present. The calculated decibel level is compared to a predetermined pass/fail limit. When a failed test is determined, a fail code is generated and the vehicle is required to be repaired and a retest performed. The predetermined decibel level, however, does not indicate that all speakers in a zone are functioning. Similarly, the predetermined pass/fail limit cannot determine if the speakers are functioning properly.
However, as vehicle sound system complexity increases and the number of speakers increase, it becomes increasingly difficult to test for the presence of all the speakers and the quality of those speakers. For example, many vehicle speakers are now wired in parallel, making it impossible to isolate and verify each speaker individually. If one of the two speakers wired in parallel is defective, the sound volume will still indicate working speakers. Thus, there is a need to increase the speed of the testing and the ability to verify that all the speakers are connected, as well as the need to determine if the speakers are performing properly.